1 Field of the Invention
The present invention relates to optical fiber-containing insulators to be mainly used for the formation of fault-localizing systems in power transmission networks and substations, and also to a producing process thereof.
2 Related Art Statement
In order to automatically localize faults in electric power systems, optical fiber-containing insulators have conventionally been used, which possess a function to transmit signals from optical sensors on a charging side to localizers on an earthed side.
FIG. 3 is a view illustrating a structural example of a voltage-current detecting system utilizing a conventional optical fiber-containing insulator. In FIG. 3, optical signals from a voltage sensor 21 and an electric current sensor 22 are transmitted to a localizer 27 through optical fibers 24-1 and 24-2 in the optical fiber-containing insulator 23, connectors 25-1 and 25-2, and couplers 26-1 and 26-2.
In this detecting system, the conventional optical fiber-containing insulator 23 is used in the state that the bared optical fibers 24-1 and 24-2 are entirely placed and sealed in an inner hole of the insulator with inorganic glass, and that opposite end faces of the insulator are finely polished to a mirror finish. The voltage sensor 21 and the current sensor 22 are bonded to the end faces through quartz ferrules 28-1 and 28-2, respectively, by using an epoxy resin. On the other hand, the optical fibers 29-1 and 29-2 on the side of the localizer 27 are bonded to the other end faces of the optical fibers through alumina ferrules 30-1 and 30-2 by using such an epoxy resin.
In the above-mentioned conventional optical fiber-containing insulator 23, the opposed end faces of the insulator containing the optical fibers must not only be mirror-polished, but also the covered optical fibers must be connected to the bared optical fibers by using the ferrules from a structural point of view. Consequently, it may be that light transmission loss occurs at the ferrule-bonded portion, and that adhesion at the ferrule-bonded portion is not sufficient. Thus, the above insulator is not satisfactory with respect to the increased number of steps and reliability.
Further, it is structurally difficult to form a plurality of optical fiber-passing paths in the conventional optical fiber-containing insulator 23, and two light-transmitting paths only can be formed therein. Therefore, since a single light-transmitting path needs to be used commonly for a light-emitting system and a light-receiving system, expensive couplers 26-1 and 26-2 need to be used for light separation. Consequently, the entire system becomes expensive.